Structured Analysis Methods and Tools. M. M. Pickard, PhD. Department of Computer Science. Overview. Methods Tools. Structured Analysis Methods. Data Models Information Flow Models Functional Models Behavior Models. Structured Analysis Tools . Data Models Entity Relationship Diagrams
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Structured Analysis Methods and Tools M. M. Pickard, PhD. Department of Computer Science
Overview • Methods • Tools
Structured Analysis Methods • Data Models • Information Flow Models • Functional Models • Behavior Models
Structured Analysis Tools • Data Models • Entity Relationship Diagrams • Data Dictionary • Information Models and Functional Models • Data Flow Diagrams • Control Flow Diagrams • Ward and Mellor Extensions • Hatley and Pirbhai Extensions
Structured Analysis Tools • Behavioral Models • Process Descriptions
Entity Relationship Diagrams • Used to show the relationship between data entities • Cardinality • relative numbers of data entities • Modality • whether data entity is required in the relationship
Data Dictionary • Purpose?
Data Dictionary • Purpose? • To define and describe all data elements • To serve as a central repository of information about the system’s data • To organize information about contents of data flows, data stores, and, possibly, external entities and processes. • Often supported by CASE tool
name aliases type length output format acceptable values formula Source security user comments Data DictionaryData element documentation
Data Dictionary (possible components) • Data flow information • Data store information • Process information • External entity information • Data structure information
Data Flow Diagram (DFD) • Shows how data moves through an information system. • Logical model • What the system does, not how it does it • Does NOT show program logic • Does NOT explicitly show processing sequence
DFD Methods • Gane and Sarson • Yourdon
DFD Symbols - Yourdon • Process • Data Flow • Data Store • External Entity
DFD - Symbols (Gane & Sarson) • Process • Data Flow • Data Store • External Entity
DFD Process Symbol • Receives input data and produces output that has a different content or form. • Process name: verb followed by a singular noun, optional adjective. Createinvoice
DFD Data Flow Symbol • A path for data to move from one part of the system to another. • Data flow name: noun and optional adjective. invoice
DFD Process Symbol rules • A process symbol must have at least one input symbol AND one output symbol. • A process symbol can have more than one input symbol and more than one output symbol. • A process can connect any other symbol.
DFD Data Flow Symbol rules • A data flow must have a process symbol on at least one end. • Avoid:
Process/Data Flow Mistakes • Spontaneous generation (miracle) • Black hole invoice Createinvoice Hours worked Calc.Grosspay Pay rate
Process/Data Flow Mistakes • Gray hole (insufficient input information to create output) Date of birth Calc.Grosspay Gross pay Pay rate
DFD - Data Store • Used to represent a situation when data must be retained in order for a process to use it later. • Data store name: plural name consisting of noun and optional adjectives Freshmen
DFD - External Entity • A person, department, outside organization, or other information system that provides data or receives output from the system. • External entity name: a singular noun bank
Control Flow Diagram • Similar to DFD • Shows control flow, not information flow • May link to CSPEC • State Transition Diagram (STD) • Process Activation Table (PAT)
Process DescriptionTools and Methods • Structured English • Decision Tables • Decision Trees
Process DescriptionTools and Methods • Structured English • Based on three building blocks of structured programming and design
Process DescriptionTools and Methods • Structured English • Based on three building blocks of structured programming and design: • sequence, selection, iteration • Uses indentation for readability and to indicate logical hierarchy • Standard, limited vocabulary
Process DescriptionTools and Methods • Decision (Logic) Tables • Used to show complex logic • Tables have four quadrants • Condition stubs • Condition entries • Action stubs • Action entries • A “rule” is a single column
Process DescriptionTools and Methods • Decision (Logic) Tables • Simplification • Rules having the same outcome, but differing by one condition may be combined. Use a dash to replace the differing condition. • Rules that have mutually exclusive conditions (cannot occur) may be carefully eliminated. • Linkage • The final action of a rule may send us to another table.
Process DescriptionTools and Methods • Decision Trees • Effective way to present a combination of simple decisions
Summary • Entity Relationship Diagrams • Data Flow Diagrams • Control Flow Diagrams • Data Dictionary • Process Descriptions